The present invention relates to a manufacturing method of a device. In more particular, the present Invention relates to the manufacturing method of a flexible device by decreasing the thickness of an insulating substrate, such as a glass substrate, and then adhering a support body such as a film onto the insulating substrate, followed by transfer of the device.
In recent years, flexible devices which are light weight and hard to crack have been increasingly required. For example, development of a flexible liquid crystal display device using a resin substrate has been progressively advanced for manufacturing a thin-film transistor liquid crystal display device. As a method for realizing the display device described above, a device manufacturing method has been already developed in which a thin-film transistor array once formed on a glass substrate is transferred to a resin substrate. For example, as the device manufacturing method described above, a method may be mentioned having the steps of wet-etching a glass substrate which has a thin-film transistor array formed thereon from a rear surface side of the glass substrate using an HF-based etching solution so that the entire glass is removed, and then adhering a resin substrate onto the above array at the etched surface side so as to form a flexible thin-film transistor array substrate (disclosed in Society for Information Display 2002 by SONY Corp).
A related process will be described with reference to FIGS. 7A to 7D, A glass substrate 14 has an etching stopper 12 and a thin-film transistor array 13 in that order on the surface thereof, A protective sheet 15 is adhered over the entire surface of the glass substrate 14 with an adhesive provided therebetween (FIG. 7A). Subsequently, the entire glass substrate is etched away from the rear surface side thereof using an HF-based etching solution 16, and the etching is stopped by the etching stopper 12 (FIG. 7B). A resin substrate 17 is adhered onto the etching stopper 12 at the etched surface side (FIG. 7C). Finally, the protective sheet 15 is peeled away, so that the transfer of the thin-film transistor array 13 is completed (FIG. 7D). Alternatively, as disclosed in Japanese Unexamined Patent Application Publication No. 11-212116, a method may be used in which the entire glass substrate is removed by a chemical polishing method instead of wet etching, followed by transfer of a thin-film transistor array to a resin substrate.
In addition, another method may also be mentioned in which a peeling layer is used instead of the etching stopper 12 shown in FIG. 7A. In the method described above, unlike the step shown in FIG. 7B, the glass substrate is not etched at all. For example, in Japanese Unexamined Patent Application Publication No. 2001-051296, an amorphous silicon layer is used as the peeling layer and is then irradiated with ultraviolet rays from a rear side surface of a glass substrate, and subsequently, the glass substrate is removed from a thin-film transistor array using the abrasion of the amorphous silicon layer. By the method described above, the transfer of the device can also be performed.
As another example of a light-weight thin film device as described above, technical development for realizing a thin IC chip has been carried out by using a method for grinding/polishing a rear surface side of a silicon wafer. For example, in Japanese Unexamined Patent Application Publication No. 9-312349, a method has been disclosed in which a silicon wafer having a semiconductor IC chip formed thereon is ground from the rear surface side, followed by transfer of the semiconductor IC chip onto a flexible resin sheet.
In the related transfer method described above, for manufacturing a flexible liquid crystal display device, after the entire glass substrate having a thin-film transistor array formed thereon is etched or polished away from the rear surface side of the substrate, the thin-film transistor array is then transferred to a resin substrate. According to this related transfer method, in the step of peeling away the protective sheet shown in FIG. 7D, in order to desirably transfer the thin-film transistor array onto the resin substrate side, peeling must be carefully performed using a long time, and as a result, the throughput is considerably decreased. In addition, after the protective sheet is peeled away, adhesive residues are allowed to remain at a thin-film transistor array portion and degrade the stability of transistor electrical characteristic, resulting in decrease in production yield. The problems described above also occur in the case in which the glass substrate is peeled away by using the peeling layer, followed by the transfer.
Furthermore, according to Japanese Unexamined Patent Application Publication No. 9-312349, the step of peeling the semiconductor IC chip from the silicon wafer and the step of transferring the IC chip to the flexible resin sheet both have a low production yield, and as a result, the manufacturing cost is inevitably increased. In addition, the application of the IC chip is limited since the IC chip has a thickness of approximately several tens micrometers and is not transparent, and since element isolation of active elements (such as transistors) is very complicated, a high-voltage element and a low-voltage element are difficult to be mounted on the same substrate.